The present invention relates to a method, an implement and a twister for tying together end portions of wire material extending around a bale.
To facilitate storage, handling and transportation of loose material, such as waste paper and cardboard, waste plastic, straw, it is usual to press the material into bales.
To prepare the bales, the material is pressed in a baling press. A baling press typically includes a baling channel in which a pressing ram is reciprocally movable to and fro, new material to be baled being added each time after the press has been retracted. The counter pressure against which the bales are pressed is obtained by resistance encountered by the material as it is pressed through the pressing channel, which, to that end, has a cross-section that decreases in downstream direction over at least a portion of its length. Initial counter pressure may be obtained by mounting obstacles in the pressing channel.
For facilitating separation of the pressed material into distinct bales and for keeping the bales together, wire material is usually tied around the bales. The wire material is usually steel wire and a loop of wire material extending around the bale is usually obtained by providing that wire material from two sources and extending along opposite sides of the bale to be formed is tied together near the downstream end of the bale to be formed and is tied together near the upstream end of the bale after the material for forming that bale has been pressed.
The tying together is usually accomplished by twisting or twining end sections of the wire material from a mutually parallel configuration.
An example of a mechanism for tying of bales is for instance described in U.S. Pat. No. 3,667,377. In this mechanism, twisters for twisting the wires are provided in the form of twisting hooks supported by a twister frame that is guided for movement vertically (i.e. towards and away from the bale) by means of hydraulic rams.
Also according to European patent application 0 808 771, twisters in the form of twist hooks are used. In this twisting mechanism separate twisters twist the wires in two engagement areas on a bale and, respectively press ram side of a needle for lifting the wires and a cutter. The twister on the press ram side of the needle engages the wires slightly later than the twister on the bale side. It is said that, in spite of the possibility of the wire to slide over the twister on the ram side, this is advantageous as it leads to shorter twisted ends, without causing the wires to be loaded dangerously prior to cutting.
U.S. Pat. No. 6,199,475 discloses twisters in the form of slotted twisting disks enclosed between plates. U.S. Pat. No. 6,032,575 discloses twisters in the form of twister pinions rotatably mounted in blocks.
Although steel wire may be tied reliably by twisting, its separation from the baled material during or after processing and even after incineration of the material is cumbersome and it can easily become entangled in processing apparatus from which it is difficult to remove. Such drawbacks would to a large extent be avoided if, instead, the bales would be tied with plastic wire, which burns up if it is incinerated and is otherwise more easily cuttable and choppable and exhibits less tendency to become entangled.
Other disadvantages of steel wire are that the twisted sections of the wire material are relatively weak compared with the strength of non twisted sections and that remainders of the material and rust forms a hazard where wire is used to bale animal feed. Where the wire is used to bale waste paper, steel material originating from the wire used to keep the bales together constitutes a separate category of waste material in the paper industry.
Plastic wire has been proposed and its use would, at least to a large extent, overcome these problems. However, plastic wire allows a much larger elastic deformation, before it is deformed plastically and therefore exhibits much more tendency to spring back and thereby untwist after twisting than steel wire. Accordingly, it is has been found difficult to connect wires of plastic material by twisting.
In International patent application WO 02/079035, it is described that untwisting and breakage of a twist of plastic threads may be avoided by reducing the distance between the position where the threads are held and the ends of the thread. To that end, the twisters are suspended in a frame that is lowered in vertical direction while the twisters continue to rotate after cutting, while the needle are lowered over twice the distance over which the frame is lowered. This, however, requires a complicated construction.